British tourists Richard and Jean Jordan strolled down to one of the popular beaches on Queensland's Hamilton Island for a mid-morning swim. It was just another blissful day - temperatures had crept up to 31C (87F) - of their holiday. Moments later, Mr Jordan walked into the Australian island's medical centre complaining he had been stung by what he thought was a jellyfish. Barely 24 hours later, he was dead.

The 58-year-old from Driffield in Yorkshire had become the first known person in the world to die after being stung by an invisible, fast-swimming jellyfish that has baffled Australian scientists for years.

The death has put the Queensland state government and tourism operators on the defensive. Mr Jordan's sister, Lesley Berry, questioned why the Queensland government had refused to fund research into the Irukandji jellyfish to find a cure for its sting. "I thought you had antivenom for all your nasties," she told Brisbane's Courier Mail.

No antidote has been found for the sting of the mysterious Irukandji, which delivers an excruciatingly painful sting but had previously not been considered a potentially killer. Now scientists are saying that the 2cm (the size of a thumbnail) jellyfish could be responsible for other deaths in Queensland.

There is no shortage of venomous creatures lurking amid the stunning tropical beaches and lush rainforests of Australia's "sunshine state", from sharks and crocodiles to beaked sea snakes, brown snakes, stone fish, blue-ringed octopus and paralysis ticks, not forgetting redback and funnelweb spiders.

The deadly box jellyfish, the most venomous marine creature in the world, is also well known and well feared. They have caused at least 67 deaths in Australia, mostly on north Queensland beaches. But while nets at beaches can project bathers from box jellyfish, and sharks, they offer no protection against the Irukandji. In a normal summer season, lifeguards on Queensland beaches will treat anything up to 20,000 sting victims, many of them from the invisible Irukandji.

Beaches have been closed across Queensland this summer after unusually warm waters and ocean currents drove thousands of the transparent Irukandji close to popular beaches. More than 80 people have been treated for serious jellyfish stings at Cairns hospital in the last two months. But amazingly little is known about the elusive jellyfish or what can combat the "Irukandji syndrome", the name given to the agonising pain that victims experience half an hour after they have been stung.

Australia's leading Irukandji expert, Dr Peter Fenner, predicted it could take another 10 years to find a cure for the sting, because there could be up to 10 different species of Irukandji responsible for causing "Irukandji syndrome".

The intense pain experienced by victims of the "Irukandji syndrome" had puzzled people for years before the jellyfish behind the sting was discovered in 1966 by Jack Barnes, a Cairns doctor who lay underwater for six hours to catch one. "You get cramping in the muscles of the legs, moving up into the abdomen, into the chest, into the arms," says Dr Fenner. "It's the really severe cramping pains that people become totally distraught by. It comes in waves, rather like labour pain, getting stronger and stronger. You need vast doses of morphine to control the pain. Victims get a really severe headache and begin vomiting. They feel absolutely dreadful. A feeling of impending doom is how they describe it".

Jack Barnes took the tiny jellyfish he had caught and tested whether it was the cause of "Irukandji syndrome" by stinging himself, his 14-year-old son and a local lifeguard. All three were rushed to hospital and survived.

Last Wednesday, Mr Jordan was flown by helicopter to Mackay base hospital, but he could not be saved. A hospital spokeswoman confirmed that he died from a cerebral haemorrhage. The sting had triggered the British man's pre-existing heart and high blood pressure problems.

Dr Fenner explains that the Irukandji sting puts pressure on the heart, potentially causing heart failure, and also pressurises the arteries and brain, which, if already brittle or damaged, can burst, causing a stroke. He fears that some deaths recorded as heart attacks in the past could have been caused by the Irukandji, and has recorded more than 800 serious stings from Irukandji in the last 18 years along the Queensland coast.

This year has been particularly bad for stings and Dr Fenner believes the thousands of Irukandji found near beaches this summer could be connected to the El Nino weather system, which alters ocean temperatures and currents. But it remains "totally impossible" to see the Irukandji in the water or predict where it might strike. "It's frightening ... especially if your business depends on it. Unfortunately some of the more unscrupulous ones will try and do a cover-up job," Dr Fenner said.

In Cairns, local newspapers have reported that beach traders and resorts have this year shied away from warning visitors about the danger of the Irukandji, but a spokeswoman for the Hamilton Island resort, where the Jordans were staying, says that the resort has been warning guests about the Irukandji since October, and, for the last two years, has encouraged visitors to swim in its seven pools rather than in the ocean.

A string of popular beaches near Cairns were closed for much of December and January because of the jellyfish, which led to complaints from many irate holidaymakers. Australia's volunteer lifeguards, the Surf Lifesavers, who are trained to warn beachgoers about "stingers" and treat stings on the beach, have also suffered abuse from visitors.

The Queensland state government has also been criticised for failing to fund Dr Fenner's research for which private funding runs out in June. The state's health department denied it was responsible for backing Dr Fenner's project and said its merit would be assessed by a federal government-funded body.

But with Dr Fenner having lodged another application for funding shortly before the death of Mr Jordan, the state government may now find it difficult to shirk the responsibility for funding the search to combat Australia's newest and most mysterious natural killer.